Air conditioning valve actuator for a motor vehicle

ABSTRACT

An air conditioning valve actuator for a motor vehicle operating on an electric step motor with a permanent magnet capable of delivering mechanical power at least equal to 50 mW, and a reduction unit for decreasing the amplitude of the angular pitch and increase the output torque. The motor is defined by the following relationship: 10 −6 &lt;γ 2 /R 0 &lt;, wherein: γ is the torque constant, proportional to the magnet volume and, R 0  is the characteristic coefficient of the volume of copper and the length of the average turn of the coils, in which R 0 =ρ.Lsp/(Scu.σ), ρ being the resistivity of copper, Lsp being the length of the average turn of a coil, Scu being the copper section of a coil and σ the filling coefficient of a coil. A controller is cooperative with the motor power supply enabling to accelerate gradually the frequency of the supply of the windings.

RELATED U.S. APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO MICROFICHE APPENDIX

Not applicable.

FIELD OF THE INVENTION

The present invention relates to an air conditioning valve actuator fora motor vehicle.

BACKGROUND OF THE INVENTION

Generally, an air-conditioning installation for a motor vehiclecomprises valves including shutters, the opening and closing of whichare motor-controlled by means of electric motors, such as stepper motorswith permanent magnets, each associated with a reduction unit.

These air-conditioning installations for motor vehicles, which can be ofthe type as disclosed in DE 4343385 and FR 2731852, have many drawbacks.Besides the problems of manufacturing costs related to the power usedand the size of the motors used, the movements of the shutters, whenopening and closing, as well as the motors themselves generate soundproblems that can difficultly be coped with through sound-insulatingmeans, since the sound waves are conveyed through the ventilationconduits.

The noise generated by the shutters and the motors is mainly due to thecharacteristics of said motors, which will be set forth hereinafter bymeans of the description of a configuration of an air-conditioningvalve-actuator for a motor vehicle, this configuration being the mostoften used one.

For reasons of simplicity and manufacturing costs for the controlelectronics, the control of this air conditioning valve actuator occursat a fixed frequency of about 200 Hz The stepper motor includes a rotorwith 6 pairs of poles, which can thus adopt 24 different positions, orsteps, per revolution. Now, in a stepper motor, to each current-supplyimpulse corresponds a constant elementary rotation by one step, so thata determined number of impulses results into a corresponding number ofsteps and, hence, into a known rotation of the rotor. Therefore, theangular distance covered by the rotor between 2 steps is 15°, so that acontrol at a fixed frequency of 200 Hz results into a rotor speed of3000°/second.

In order for this speed to be usable, the motor is associated with areduction unit the gear train of which allows increasing the outlettorque and reducing the amplitude of the angular pitch. By using areduction unit with a ratio of about 300, the fixed speed of rotation ofthe air-conditioning shutter is about 10°/second.

This being said, the need for an operation according to a so called“start-stop” mode, i.e. for instantaneously switching over, between twosuccessive steps of the motor, in its starting phase, from 0 to 200 Hz,requires dimensioning the motor so that it be capable of acceleratingthe shutter inertia of said air-conditioning shutter and the rotor's owninertia within a time period close to 5 milliseconds, which correspondsto the duration of one step.

Now, in a “start-stop” operating mode, the torque of the motor isclearly lower than that of the same motor operating in the dynamic mode,since in the latter there is no need for an instantaneous accelerationof the inertia of the rotor and that of the air-conditioning shutter.

Therefore, in order to reach, at the outlet of the reduction unit, thetorque required for moving an air-conditioning shutter in a“start-stop”-type operation, it is necessary to oversize the motor.

Furthermore, with a coil resistance maintained constant, the availablemechanical power, the torque and the electric-power consumptionextremely quickly increase with the power-supply voltage. Now, theair-conditioning valve has been designed so as to carry out its missionalso at a degraded 8-Volt battery voltage, i.e. the torque required formoving the air conditioning shutter should also be reached at an 8-Voltvoltage. The voltage of a non-controlled battery however varies between8 and 14 Volt, so that the motor mostly operates at a voltage higherthan 8 Volt, which, because of the increase in available mechanicalpower, torque and electric-power consumption, besides the increasednoise, is also prejudicial to the valve's lifetime, since this causes,on the one hand, at the level of the reduction unit, an excessiveblocking torque likely to damage the toothing of the latter and, on theother hand, an overheating of the winding of the motor.

Furthermore, in the field of the air-conditioning valve-actuators, theuse of stepper motors requires, at each start, a re-initializationachieved by bringing the shutter of the valve into abutment. In the“start-stop” operating mode at 200 Hz, the valves generate acharacteristic noise when the valve arrives in abutment, since thestepper motor is still at its synchronism speed and the rotor startsvibrating at about the stop position. Since the reduction unit isslightly elastic, the motor even accumulates energy while setting thistype of spring formed by the gears and, in some applications, one caneven see that the motor turns back by some tens of steps, under theaction of this elasticity, when the current supply has been interruptedin the windings.

BRIEF SUMMARY OF THE INVENTION

The present invention is aimed at coping with the variousabove-mentioned drawbacks by providing an air-conditioningvalve-actuator for a motor vehicle that, compared to the existingactuators, while meeting the minimal requirements of the application,generates less noise when in operation, has a higher efficiency and hasa smaller size and weight, which represents a non-negligible costsaving.

The air-conditioning valve-actuator for a motor vehicle implements anelectric motor such as a stepper motor with permanent magnet capable ofdelivering mechanical power at least equal to 50 mW, as well as areduction unit allowing reducing the amplitude of the angular pitch andincreasing the outlet torque, and it is mainly characterized in thatsaid motor is defined by following relationship: 10⁶−6<γ²/R₀<50⁶, where

-   -   γ is the torque constant, expressed in Nm/At, proportional to        the magnet volume and,    -   R₀ is the characteristic coefficient of the volume of copper and        the length of the average turn of the coils, expressed in        Ohm/tr², R₀=ρ.Lsp/(Scu.σ), ρ being the resistivity of copper,        Lsp being the length of the average turn of a coil, Scu being        the copper section of a coil and σ the filling coefficient of a        coil;    -   and in that it comprises means for controlling the power-supply        to said motor allowing to gradually accelerate the frequency of        power-supply to the windings to reach a working frequency of        said motor higher than the “start-stop” starting frequency.

It is known that the motors of the air-conditioning valve actuators formotor vehicles have a dynamic torque given by following formula:$T_{th} = {{k\frac{\gamma \cdot {ni}_{0}}{\sqrt{1 + \left( {\tau_{e}\omega_{e}} \right)^{2}}}} - \frac{{\alpha\gamma}^{2}}{R_{0}\left\lbrack {1 + \left( {\tau_{e}\omega_{e}} \right)^{2}} \right\rbrack}}$

-   -   where T_(th) is the torque at a given speed, expressed in Nm        -   π_(e) is the electric time constant, expressed in m.s        -   ω_(e) is the electric pulse, expressed in rad/s        -   α is the mechanical speed, expressed in rd/s        -   ni₀ is the number of Ampere-turns per coil at zero speed        -   K is a coefficient the value of which depends on the current            supply mode and the type of motor, two-phase or three-phase.

This formula can also be written as follows:$T_{th} = {{k\frac{\gamma\sqrt{\frac{p_{c}}{R_{0}}}}{\sqrt{1 + \left( {\tau_{e}\omega_{e}} \right)^{2}}}} - \frac{{\alpha\gamma}^{2}}{R_{0}\left\lbrack {1 + \left( {\tau_{e}\omega_{e}} \right)^{2}} \right\rbrack}}$

-   -   where Pe represents the electric-power dissipation in a phase of        the motor.

It should be noted that each of both terms of this expression isproportional to the γ²/R₀ factor, which can be used to define the motorswith permanent magnet, since the torque constant γ is proportional tothe magnet volume, whereas coefficient R₀ is inversely proportional tothe copper volume.

One should note that the motors presently used in the air-conditioningapplications and the current-supply frequency of which is 200 Hz have aγ²/R₀ factor the value of which is close to 100^(6−6.)

Therefore, for a valve actuator according to the invention, the γ²/R₀factor of which is between 10⁶−6 and <50⁶−6, a mechanical power at leastequal to 50 mW can be achieved only at a high current-supply frequency,about twice that of the motors presently used.

Of course, the reduction ratio should be changed proportionally.

Since the torque constant γ is proportional to the magnet volume and theR₀ coefficient is inversely proportional to the copper volume, thereduction of the γ²/R₀ factor results, for identical performances interms of mechanical power, into a considerable reduction of the magnetand copper volume, which has, in addition, an incidence on themanufacturing costs, into a reduction in weight and into a reduction ofthe vibrations and the noise, because of the reduction of the motorinertia.

On the other hand, due to the characteristics of the motor, the highcurrent-supply frequency does not allow a classical “start-stop”operation; it is therefore absolutely necessary to proceed, through acontroller, to a gradual increase of the current-supply frequency,starting from a sufficiently low frequency for allowing separating theshutter.

According to an additional feature of the actuator according to theinvention, it includes a controller for controlling the power of thecurrent supply to the motor.

Such controller allows allow, for example, maintaining the averagevoltage as seen by the motor at a constant value, which is preferably 8Volt.

According to a preferred embodiment of the actuator according to theinvention, the motor is a three-phase motor with star or deltaconnection, driven by six transistors.

According to the invention, the rotor speed of the motor is at least5400 degrees per second, while the reduction ratio is higher than 540.

Further advantages and features of the actuator according to theinvention will clearly appear from the following description, withreference to the attached drawing that show several non-restrictiveembodiments of it.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a graph showing the available torque of the motor of anair-conditioning valve actuator presently used, when operating in“start-stop” mode.

FIG. 2 is a graph showing the dynamic torque and the mechanical power ofthe same motor when operating in dynamic mode.

FIG. 3 is a graph showing the dynamic torque and the mechanical powerwhen operating in dynamic mode for a similar motor at a higherpower-supply voltage.

FIG. 4 is a graph showing the mechanical power as a function of thetorque constant of a similar motor at various speeds of rotation of therotor.

FIG. 5 is a graph showing the power-supply frequency in the “start-stop”operating mode.

FIG. 6 is a graph showing the power-supply frequency for the motor of anair conditioning valve actuator for a motor vehicle according to theinvention.

FIG. 7 is a perspective and exploded view of a first embodiment of themotor of the actuator according to the invention.

FIG. 8 is a perspective view of a second embodiment of the motor of thesame actuator.

FIG. 9 is a perspective and exploded view of a third embodiment of themotor of the same actuator.

FIG. 10 shows a diagrammatic illustration of the control mode for themotor described in FIG. 9.

FIG. 11 is a table showing the various power-supply sequences for thesame motor.

DETAILED DESCRIPTION OF THE INVENTION

When referring to FIG. 1, one can see the evolution of the availabletorque when instantaneously switching over from 0 Hz to any value ofspeed, i.e. in the “start-stop” operating mode, for a stepper motor withpermanent magnet the air-conditioning valve actuators for a motorvehicle are provided with, which is standard for it and thecharacteristics of which are: 24 steps/revolution, 200 Hz current-supplyfrequency, 8-Volt voltage and 100-Ohm coil resistance.

When referring to FIG. 2, one can see, for the same motor, the evolutionof the available torque for any set speed, i.e. in the dynamic operatingmode.

When comparing these two graphs, one notices of course that at 200 Hzthe dynamic torque is clearly higher than the “start-stop” torque, sincethey are about 2 and 4 mNm.

A 2 mNm “start-stop” torque provides, at the outlet of a {fraction(1/300)} reduction unit with a 70% efficiency, a 420 mNm useful torqueat a voltage of 8 volts, which corresponds to the torque required for anair-conditioning valve at that current-supply voltage.

Thus, one sees that this stepper motor is oversized to be capable ofoperating in the “start-stop” mode at 200 Hz. The mechanical powerrequired for the air-conditioning application is indeed of 420mNm×10°/second, i.e. 50 mW and is also shown in FIG. 2, by aninterrupted line, whereby the mechanical power, expressed in Watt, canbe delivered by the motor at a fixed 200 Hz speed, always at an 8 Voltcurrent-supply voltage. One can see that at 200 Hz, the power is 220 mW,i.e. about twice the power required for the application, when takinginto consideration a 70% efficiency of the reduction unit.

When referring now to FIG. 3, one can see a graph similar to that ofFIG. 2, for an identical motor, except that its current-supply voltageis 14 Volt.

When comparing these two graphs, one can see that, with a coilresistance maintained constant, the available mechanical power, thetorque and the electric-power consumption quickly increase as thecurrent-supply voltage increases.

As has been set forth above, the motor is designed to operate with adegraded 8-Volt battery, which however permanently supplies a muchhigher current-supply voltage, so that the excess performances of themotor, when the voltage is higher than 8 Volt, are not used and aretherefore not necessary and, in addition, they are prejudicial to thevalve's lifetime and are a source for additional noise problems.

When referring now to FIG. 4, one can see a graph that shows, for an8-Volt two-phase motor, the mechanical power as a function of γ, themotor's torque constant, at several speeds, hence at severalcurrent-supply frequencies, curves A, B and C showing speeds of 600, 400and 200 steps/second, respectively. It clearly appears from this graphthat the higher the torque constant γ, the lower the speed of rotationat which the maximum power is achieved.

It can also be observed that it is possible to achieve mechanical powersat the outlet of the motors very close to each other with very differenttorque constants, at different speeds of rotation.

Therefore, assuming that the mechanical power necessary for theapplication is close to 50 mW, that the efficiency of the reduction unitis close to 0.5 and that iron losses should be taken into consideration,the mechanical power required at the level of the motor is close to 0.15Watt, irrespective of the current-supply voltage. It can be seen thatthis mechanical power at the level of the motor can be achieved by amotor with a torque constant of 2,5⁶−5 Nm/At rotating at 600steps/second as well as by a motor with a torque constant of 4⁶−5 Nm/Atrotating at 200 steps/second, which corresponds to the motors presentlyused.

The air-conditioning valve actuator for a motor vehicle according to theinvention includes a motor the rotor speed of which is higher than 5400degrees per second, as well as a reduction unit the reduction ratio ofwhich is therefore, and preferably, higher than 540.

In addition, from the relationship:$T_{th} = {{k\frac{\gamma\sqrt{\frac{p_{c}}{R_{0}}}}{\sqrt{1 + \left( {\tau_{e}\omega_{e}} \right)^{2}}}} - \frac{{\alpha\gamma}^{2}}{R_{0}\left\lbrack {1 + \left( {\tau_{e}\omega_{e}} \right)^{2}} \right\rbrack}}$

-   -   it is known that the torque of a motor at a given speed is        proportional to the γ²/R₀ factor, therefore, the        air-conditioning valve actuator according to the invention is        defined by a γ²/R₀ factor between: 10⁶−6 and 50⁶−6.

Since the acceleration torque necessary to accelerate the inertia of therotor and the inertia of the shutter, at high current-supply frequency,is higher than the torque available on a motor of such a size, in the“start-stop” operating mode, it is necessary to define another operatingmode.

In FIG. 5 has been shown the current-supply frequency in the“start-stop” operating mode, which has to be compared with that of thechosen operating mode shown in FIG. 6.

This operation mode, called “ramping mode”, allows implementing agradual acceleration of the frequency, until reaching the requiredfrequency, while starting from a frequency that allows the motor todeliver the necessary accelerating torque for accelerating the inertiaof the rotor and the inertia of the shutter, that means that before theacceleration the operating mode is similar to a “start-stop” mode.

This operating mode has another advantage, at the level of there-initialization. With a motor of a valve actuator according to theinvention operating above the “start-stop” speed, when the shutterstrikes against the stop, the motor indeed automatically loses itssynchronous speed. When synchronism is lost at high speed against thestop, the setting and kick back phenomenon noticed with the existingactuators is strongly attenuated, because the rotor cannot restart in asynchronous way, since the energizing frequency is higher than the“startstop” speed and the dynamic torque present at the moment of theshock is smaller.

Because of the small size of the motor used in the actuator according tothe invention, the electric power supplied to the inlet of the motor hasto be controlled, in order not to let the current-supply voltage varybetween 8 and 14 Volt, and to limit the Joule power dissipation in thewindings of the motor.

The actuator according to the invention allows detecting the value ofthe current-supply voltage and controlling, by means of a choppingtechnique, the percentage of this voltage applied to the windings of themotor. By way of an example, the ratio will be 100% for an 8 Voltcurrent-supply voltage and 57% for a 14 Volt current-supply voltage.

This chopping technique furthermore allows reducing the current when atstop; when no shutter-movement function is required, a limited-operationfactor, for example 10%, can indeed be applied, in order to maintain thevalve in its position.

Moreover, this technique also allows, during the acceleration anddeceleration phases, which are very limited in time, about 50 ms, toapply a 100%-operation factor and to switch over again to anormal-operation factor during the movements at constant speed.

The stepper motor with permanent magnet of an air-conditioningvalve-actuator for a motor vehicle according to the invention can be ofvarious types, some of which are shown in FIGS. 7, 8 and 9.

In FIG. 7 is shown a two-phase motor 1 with a deep-drawn plate with a 20mm outer diameter, 24 steps/revolution, operating at 400 Hz and coupledto a reduction unit 2 the reduction ratio of which is close to 600. Byway of comparison, for the same function, a motor of the same typeoperating at 200 Hz, but with a 35 mm diameter, is presently used.

When referring now to FIG. 9, one can see the preferred embodiment ofthe gear motor of an actuator according to the invention. It includes athree-phase motor 11 with permanent magnet, 30 steps/revolution, having5 pairs of poles at the rotor, operating at 450 Hz and coupled to areduction unit 21 the reduction ratio of which is close to 540.

The three-phase motor allows, for the same digital phase-switching mode,two fed phases, a higher resolution than the motors shown in FIGS. 7 and8 that allow resolution modes of 20 and 24 steps per revolution,respectively, whereas the motor shown in FIG. 9 has a resolution of 30full steps per revolution. The noise and vibrations of the motor duringoperation will thus be reduced.

On the other hand, the digital phase-switching mode of the three-phasemotor can be carried out by means of only six transistors, whereas eighttransistors are necessary for the bipolar two-phase motors (currentflowing in the coil of one phase in both directions).

Where referring now to FIG. 10, one can see that the preferred controlmode for example consists in connecting the three-phase motor accordingto the “star” connection, by successively feeding two by two the phasesA, B, C according to a sequence described in FIG. 11. A “2 phases ON”current supply used on a three-phase motor allows a 20% torque gain,compared to the same control mode used on a two-phase motor, 1.414 timesthe 1-phase-ON torque. In addition, the change in the torque between 2phase switchings is smaller in a three-phase motor than in a two-phasemotor, which will cause a lesser change in rotor speed during operation.

The control of an air-conditioning valve actuator for a motor vehicle bymeans of a three-phase motor thus provides, compared to a two-phasemotor:

-   -   less noise and vibrations, thanks to the reduction of the torque        undulation and to the increase of the resolution,    -   a cheaper electronic control, and    -   a better efficiency, because of the increased available toque        for the same electric power at the inlet.

On the other hand, such a three-phase motor requires only threecurrent-supply threads, whereas a two-phase motor requires four of them.

1. An air conditioning valve actuator for a motor vehicle comprising: astepper motor means having a permanent magnet with a mechanical poweroutput of at least 50 mW, said stepper motor means for producing anangular pitch and an outlet torque, said stepper motor means having avolume of copper therein and a length of the copper in coils, saidstepper motor means having a working frequency and a starting frequency;a reducing means cooperative with said stepper motor means for reducingan amplitude of the angular pitch and for increasing the outlet torque,said stepper motor means defined by relationship of 10⁻⁶<γ²/R₀<50⁻⁶where γ is the torque constant proportional to a volume of saidpermanent magnet, R₀ is a characteristic coefficient of the volume ofcopper and the length of the average turn of the coils, R₀=ρLsp/(Scu.σ)in which ρ is a resistivity of copper and in which Lsp is a length ofthe average turn of a coil and in which Scu is a copper section of thecoil and in which σ is a filling coefficient of the coil; a power supplyconnected to said stepper motor means, said power supply having afrequency and a current supply; and controlling means interactive withsaid power supply and said stepper motor means, said controlling meansfor gradually accelerating the frequency of said power supply to thecoils of said stepper motor means to reach the working frequency of saidstepper motor means, said working frequency being higher than saidstarting frequency.
 2. The structure of claim 1, said power supplyhaving meas for controlling a power of the current supply to saidstepper motor means.
 3. The structure of claim 1, said stepper motormeans being a star-connected three-phase motor driven by sixtransistors.
 4. The structure of claim 1, said stepper motor means beinga delta-connected three-phase motor driven by six transistors.
 5. Thestructure of claim 1, said stepper motor means having a rotor speed ofat least 5400 degrees per second, said reducing means having a reductionratio of greater than 540.